Thioethers xanthates

Since alkyl halides can be converted to mercaptans, thioethers, xanthates, or thiouronium compounds, the ready removal of these groups offers another... 

The Leuckart Thiophenol Reaction allows the preparation of thiophenols and corresponding thioethers from anilines or their corresponding diazonium salts. The first step is the reaction of an aryl diazonium salt with a potassium alkyl xanthate to give an aryl xanthate, which affords an aryl mercaptan upon basic hydrolysis or an aryl thioether upon warming. 

The initiation step (i) producing the tributyltin radical can be performed by thermolysis of radical initiators such as AIBN. Complementarily, the use of a Et3B/02 system or of photochemical irradiation allows the reactions to proceed at low temperature. The reaction (ii) with the substrate forming the carbon radical applies the same substrates as those used in tin hydride chemistry, such as iodides, bromides, selenides xanthates and even thiocarbonates. Furthermore, the possible competitive addition of tributyltin radicals to the allyltin reagent is of no consequence due to the rapid /3-fragmentation of the resulting carbon-centred radical, which renders this reaction a degenerate one. It is noteworthy that less reactive radical precursors such as chlorides or phenyl thioethers can be used efficiently. The evolution of the radical (iii) via several intra- or intermolecular elementary... 

There has been a review of the use of transition-metal catalysts in the formation of C—S, C—Se, and C—Te bonds." Copper catalysis enables the formation of unsymmetrical diaryl thioethers from two differently substituted aryl iodides using ethylxanthogenate as the source of sulfur. Initial formation of an aryl xanthate, such as (17), is followed by hydrolysis to the arenethiolate, which couples with the second aryl iodide." Copper catalysis has also been used in the methylthiolation of aryl halides by DMSO. The method requires the presence of a source of fluoride ions, such as zinc fluoride." In the presence of a palladium catalyst, the reaction of aryl and heteroaryl bromides with AgSCp3 gives the corresponding trifluoromethylsulfldes." ... 

Decomposition of diazoxanthates, by warming gently in faintly acidic cuprous media, to the corresponding aryl xanthates which afford aryl thiols on alkaline hydrolysis and aryl thioethers on warming ... 

---